Homogeneous charge compression ignition engine and air intake and exhaust system thereof

ABSTRACT

An EGR passage partially refluxes exhaust gas to a combustion chamber as an EGR gas. A heat exchanger cools the EGR gas. A heating intake passage branches off from a branching portion formed in a portion of an intake passage on an upstream side of a downstream end of the EGR passage, and its downstream end communicates with a portion of the EGR passage on an upstream side of the heat exchanger. A switch valve adjusts respective amounts of intake air passing through the intake passage and through the heating intake passage. When an EGR valve is closed, an ECU switches the switch valve such that the intake air passes through one of the intake passage and the heating intake passage; when the EGR valve is open, the ECU switches the switch valve such that the intake air passes solely through the intake passage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a homogeneous charge compressionignition engine and an air intake and exhaust system thereof forrefluxing exhaust gas to a combustion chamber as an EGR gas.

2. Description of the Related Art

In recent years, in the field of internal combustion engines, attentionis being given to a homogeneous charge compression ignition enginecapable of attaining a satisfactory fuel efficiency and thermalefficiency, and various studies are being conducted in this regard. Inmost homogeneous charge compression ignition engines, fuel and air aremixed with each other in an intake passage, and the resultant air fuelmixture is supplied to a combustion chamber. Further, the air fuelmixture trapped in the combustion chamber undergoes self-ignition duringcompression stroke with an increase in temperature and pressure due torising of a piston. As is known in the art, in such a homogeneous chargecompression ignition engine, the operation range allowing stable controlof the homogeneous charge compression ignition (HCCI) is still rathersmall, which is a problem to be solved in putting this engine intopractical use. In view of this, with a view toward solving this problem,an attempt is being made to put into practical use a homogeneous chargecompression ignition engine as applied to a stationary engine whosenormal operation range is relatively small, such as a gas heat pump(GHP) gas engine. Further, there has also been proposed an engine inwhich operational switching is effected as appropriate such thathomogeneous charge compression ignition is effected in a range near alow/medium rotation and low/medium load range, which is frequentlyadopted in actual operation, and that spark ignition (SI) is effected ina high rotation range and an ultra-low load and high load range.

In a homogeneous charge compression ignition engine, the operation rangeallowing stable control of the homogeneous charge compression ignitionis small. In the following, this problem will be discussed in detail.For example, in the low load operation range, the amount of air fuelmixture supplied to the combustion chamber is small, and the in-cylindertemperature does not easily increase, so the ignition propertydeteriorates, and a misfire is liable to occur. As is known in the art,in order to suppress occurrence of a misfire, there is adopted a methodusing a so-called internal EGR, according to which a negativeoverlapping period is provided in the valve timing of the intake valveand the exhaust valve so that a part of the gas already burnt may beallowed to remain in the combustion chamber for the next cycle ofcombustion. By thus utilizing the internal EGR, the internal EGR gas athigh temperature and the air fuel mixture newly supplied to thecombustion chamber are mixed with each other to increase the in-cylindertemperature, so the ignition property at the time of homogeneous chargecompression ignition is improved, thus suppressing occurrence of amisfire. However, under a still worse condition as in the case of a lowoutdoor air temperature, the temperature in the combustion chamber islow, and a high-temperature internal EGR is hard to obtain, so even whenan internal EGR is used, homogeneous charge compression ignition israther hard to effect, and there is a fear of occurrence of a misfire.

Apart from the internal EGR, there is known, as a means for increasingthe in-cylinder temperature of the combustion chamber of, for example, adiesel engine, a means which prevents occurrence of a misfire by causingheated intake air (air fuel mixture) previously heated by a heatingmechanism such as a heat exchanger to flow into the combustion chamber,that is, by performing intake air heating.

On the other hand, in a homogeneous charge compression ignition engine,there occurs in the high load operation range an abnormal combustionsuch as knocking or premature ignition. As is known in the art, in orderto suppress occurrence of such an abnormal combustion, there is utilizedan external exhaust gas recirculation (EGR). Since the external EGR gasimmediately after its extraction from the exhaust passage is at hightemperature, it is cooled by an EGR cooler provided at some midpoint inthe EGR passage so that the volumetric efficiency of the intake air maynot be deteriorated. Further, by refluxing the EGR gas cooled by the EGRcooler into the combustion chamber, the combustion in the combustionchamber is slowed down due to an increase in inert gas.

As an example of the heat exchanger as the heating device or the heatexchanger as the EGR cooler, JP 2005-517857 A cited herein as PatentDocument 1 discloses a technique according to which the heating of theintake air and the cooling of the external EGR gas are effected by usinga heat exchanger 12 (see FIG. 2 of Patent Document 1 described above).In this technique, the heat exchange mechanism is made relatively simpleby effecting the cooling of the EGR gas and the intake air heating withthe same coolant.

However, while having a single casing, the heat exchanger of PatentDocument 1 described above contains a first heat exchange portion and asecond heat exchange portion that are separate from each other, and thecooling of the EGR gas and the intake air heating are effected in eachof those separate systems, i.e., within each of the first heat exchangeportion and the second heat exchange portion. Thus, while it can achievespace saving as compared with the related-art technique using two heatexchangers, the technique as disclosed in Patent Document 1 describedabove involves an increase in size of the heat exchanger as comparedwith an ordinary heat exchange system consisting of a single heatexchanger. Further, in an internal combustion engine using the heatexchanger of Patent Document 1 described above, it is necessary toconnect to the single heat exchanger a large number of pipes, includingpipes constituting the intake passage and the EGR passage and a pipe forcoolant, resulting in a rather strict limitation in terms of design inarranging them around the internal combustion engine.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to provide ahomogeneous charge compression ignition engine and an air intake andexhaust system thereof which help to achieve further space saving andwhich allow EGR gas cooling and intake air heating.

In order to achieve the above-mentioned object, a homogeneous chargecompression ignition engine according to the present invention includes:a combustion chamber; an intake passage serving as a passage for intakeair to the combustion chamber; an exhaust passage serving as a passagefor exhaust gas from the combustion chamber; an EGR passage,communicating with the exhaust passage and the intake passage, forrefluxing a part of the exhaust gas from the combustion chamber to thecombustion chamber as an EGR gas; a heat exchanger, provided at somemidpoint in the EGR passage, for cooling the EGR gas; an EGR valve,provided at some midpoint in the EGR passage, for adjusting an openingand closing of the EGR passage; a heating intake passage which branchesoff from a branching portion formed in a portion of the intake passageon an upstream side of a downstream end of the EGR passage and whosedownstream end communicates with a portion of the EGR passage on anupstream side of the heat exchanger; a switch valve for adjustingrespective amounts of intake air passing through the portion of theintake passage on a downstream side of the branching portion and throughthe heating intake passage; and a control means which, when the EGRvalve is closed, switches the switch valve such that, on the downstreamside of the branching portion, the intake air flowing into thecombustion chamber passes through at least one of the intake passage andthe heating intake passage, and which, when the EGR valve is open,switches the switch valve such that, on the downstream side of thebranching portion, the intake air flowing into the combustion chamberpasses solely through the intake passage.

Further, in order to achieve the above-mentioned object, an air intakeand exhaust system for use in a homogeneous charge compression ignitionengine according to the present invention is used for a homogeneouscharge compression ignition engine having a combustion chamber and anexhaust passage serving as a passage for exhaust gas from the combustionchamber. The air intake and exhaust system includes: an intake passageleading to the combustion chamber; an EGR passage, communicating withthe exhaust passage and the intake passage, for refluxing the exhaustgas from the combustion chamber to the combustion chamber as an EGR gas;a heat exchanger, provided at some midpoint in the EGR passage, forcooling the EGR gas; an EGR valve, provided at some midpoint in the EGRpassage, for opening and closing the EGR passage; a heating intakepassage which branches off from a branching portion formed in a portionof the intake passage on an upstream side of a downstream end of the EGRpassage and whose downstream end communicates with a portion of the EGRpassage on an upstream side of the heat exchanger; a switch valve foradjusting respective amounts of intake air passing through the intakepassage and through the heating intake passage on a downstream side ofthe branching portion; and a control means which, when the EGR valve isclosed, switches the switch valve such that, on the downstream side ofthe branching portion, the intake air flowing into the combustionchamber passes through at least one of the intake passage and theheating intake passage, and which, when the EGR valve is open, switchesthe switch valve such that, on the downstream side of the branchingportion, the intake air flowing into the combustion chamber passessolely through the intake passage.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings;

FIG. 1 is an overall schematic view of a homogeneous charge compressionignition engine and an air intake and exhaust system thereof accordingto an embodiment of the present invention;

FIG. 2 is a chart illustrating how an EGR valve and a switch valve ofthe homogeneous charge compression ignition engine of FIG. 1 arecontrolled;

FIG. 3 is a schematic view of the operation ranges when the homogeneouscharge compression ignition engine of FIG. 1 is used;

FIG. 4 is an overall schematic view of a first modification of thehomogeneous charge compression ignition engine of FIG. 1;

FIG. 5 is an overall schematic view of a second modification of thehomogeneous charge compression ignition engine of FIG. 1; and

FIG. 6 is an enlarged schematic view illustrating an operation rangeallowing homogeneous charge compression ignition without using anysupercharger in the homogeneous charge compression ignition engine ofFIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following, a preferred embodiment of the present invention willbe described with reference to the drawings.

(Overall Construction)

With reference to FIG. 1, the overall construction of a homogeneouscharge compression ignition engine and an air intake and exhaust systemthereof according to an embodiment of the present invention will bedescribed. In the following description, the term “intake air” means agas supplied into a combustion chamber (e.g., mixture of intake air andgas fuel or mixture of intake air, gas fuel, and external EGR), and theterm “air fuel mixture” means a mixture of intake air and gas fuel.

As shown in FIG. 1, a homogeneous charge compression ignition engine 1has a combustion chamber 10, an intake passage 11 p leading to thecombustion chamber 10, and an exhaust passage 12 p constituting apassage for the exhaust gas from the combustion chamber 10, and effectsswitching as appropriate between spark ignition and homogeneous chargecompression ignition according to the operating conditions (load andengine RPM). In this way, by switching between homogeneous chargecompression ignition and spark ignition according to the operatingconditions, it is possible to attain both the high fuel efficiency dueto homogeneous charge compression ignition and the satisfactory startingproperty and high output due to spark ignition.

Further, the homogeneous charge compression ignition engine 1 has asupercharger 11 t, a throttle 3, a fuel valve 2 v (fuel supply amountadjusting device), a heating intake passage 20 p, a switch valve 11 v,an EGR passage 30 p, an EGR valve 30 v, a heat exchanger 40, an intakevalve 51 v, an exhaust valve 52 v, and an ignition plug 53 c. (Thosecomponents will be described in detail below). Further, the homogeneouscharge compression ignition engine 1 has an electronic control unit(ECU, which corresponds to a control device) 5. Electrically connectedto the ECU 5 are control cables 5 a through 5 i corresponding to theexhaust valve 52 v, the ignition plug 53 c, the intake valve 51 v, theEGR valve 30 v, the switch valve 11 v, the throttle 3, the fuel valve 2v, a bypass control valve 40 v, and the supercharger 11 t, respectively.Further, the ECU 5 controls the operation of the exhaust valve 52 v, theignition plug 53 c, the intake valve 51 v, the EGR valve 30 v, theswitch valve 11 v, the throttle 3, the fuel valve 2 v, the bypasscontrol valve 40 v, and the supercharger 11 t.

(Regarding the Air Intake and Exhaust System)

An air intake and exhaust system 60 of the homogeneous chargecompression ignition engine 1 of this embodiment is used to supplyintake air to the combustion chamber 10, to scavenge exhaust gas fromthe combustion chamber 10, etc., and includes the intake passage 11 p,the exhaust passage 12 p, the heating intake passage 20 p, the switchvalve 11 v, the EGR passage 30 p, the EGR valve 30 v, the heat exchanger40, and the ECU 5. Further, apart from the above-mentioned intake airsupply, etc., the air intake exhaust system 60 performs mixing ofexternal EGR with air fuel mixture, intake air heating, etc.

(Mixer)

The homogeneous charge compression ignition engine 1 has a mixer 4 atsome midpoint in the intake passage 11 p; a gas fuel is supplied to themixer 4 through a fuel supply path 2 p communicating with the mixer 4.(That is, fuel supply path 2 p serves as the passage for the gas fuel,and communicates with intake passage 11 p). Further, air and the fuelare mixed with each other at the mixer 4.

(Fuel Valve)

The fuel valve 2 v is provided at some midpoint in the fuel supply path2 p. Further, under control of the fuel valve 2 v by the ECU 5, thedegree of opening of the fuel valve 2 v is adjusted, whereby the amountof gas fuel supplied to the intake passage 11 b is adjusted.

(Throttle)

As shown in FIG. 1, the throttle 3 has a step motor (not shown) fordriving a shaft 3 c and a valve portion 3 v, and the valve portion 3 cis rotatable around the shaft 3 c. Further, the ECU 5 controls the stepmotor of the throttle 3, whereby the degree of opening of the passage isadjusted by the valve portion 3 v, thereby adjusting the amount ofintake air supplied to the combustion chamber 10 through the intakepassage 11 p.

(Supercharger)

The supercharger 11 t is of an electric turbo type whose superchargingpressure is variable, and is formed as a centrifugal compressor drivenby an electric motor M. The supercharger 11 t is arranged at somemidpoint in the intake passage 11 p. Further, a bypass route 40 a and amain route 40 b are respectively connected to the upstream side of thesupercharger 11 t and to the outlet portion of the supercharger 11 t,and communication through those routes is provided for the intakepassage 11 p. At some midpoint of the bypass route 40 a, there isprovided a bypass control valve 40 v for opening and closing the bypassroute 40 a.

When the supercharger 11 t is not used, the electric motor M iscontrolled to be kept at rest, and the bypass control valve 40 v iscontrolled to be kept open. As a result, the bypass route 40 a functionsas a normal intake passage. On the other hand, when performingsupercharging by using the supercharger 11 t, the electric motor M iscontrolled to be driven to be rotated, and the bypass control valve 40 vis controlled to be closed. As a result, the main route 40 b functionsas a supercharging passage.

(Combustion Chamber)

The combustion chamber 10 is an internal space defined in the internalcombustion engine by a cylinder and a piston; a piston 50 reciprocatesvertically as seen in the drawing. The air fuel mixture is supplied tothe combustion chamber 10 through the intake passage 11 p. After thecombustion, the exhaust gas is discharged through the exhaust passage 12p. The intake valve 51 v and the exhaust valve 52 v are arranged at theopening of the intake passage 11 p to the combustion chamber 10 and atthe opening of the exhaust passage 12 p to the combustion chamber 10,respectively. Those valves are opened and closed as appropriate uponrising and lowering of the piston 50 during the strokes of intake,compression, combustion/expansion, and exhaust, thereby effecting intakeand exhaust. More specifically, the intake valve 51 v and the exhaustvalve 52 v are respectively driven to be opened and closed by cams 51 cand 52 c formed on the outer peripheries of camshafts (not shown), andtheir opening/closing timing (phase with respect to the crank angle) isvaried by a well-known variable valve timing mechanisms provided on thecamshafts. The ignition plug 53 c is used for ignition at the time ofspark ignition, and its operation is controlled by the ECU 5.

(EGR Passage)

The exhaust gas from the combustion chamber 10 passes through theexhaust passage 12 p, and is discharged to the exterior through anexhaust port (not shown); a part of the exhaust gas discharged into thedischarge passage 12 p is supplied to the combustion chamber 10 again.The EGR passage 30 p serves to reflux a part of the exhaust gas from thecombustion chamber 10 to the combustion chamber 10 as EGR gas; itbranches off from the exhaust passage 12 p at a branching position 12 b,and a downstream end 30 b thereof communicates with the intake passage11 p. As a result, the inner space of the exhaust passage 12 p and thatof the intake passage 11 p communicate with the inner space of the EGRpassage 30 p at the upstream end (branching position 12 b) and thedownstream end 30 b of the EGR passage 30 p.

Halfway through the EGR passage 30 p, there are provided the EGR valve30 v for adjusting the opening/closing condition of the EGR passage 30 pand the heat exchanger 40 for cooling the EGR gas in that order from theupstream side (with respect to the flowing direction of the EGR gas).Further, as described below, the EGR passage 30 p has a communicatingportion 20 b between the EGR valve 30 v and the heat exchanger 40,establishing communication with the downstream end of the heating intakepassage 20 p.

(Heat Exchanger)

The heat exchanger 40 is provided at some midpoint in the EGR passage 30p, and functions as a cooling device for the EGR gas. Further, in thecase where the switch valve 11 v has been switched so as to allowpassage of intake air (air fuel mixture) through the heating intakepassage 20 p, the heating exchanger 40 also functions as an intake airheating device.

The heat exchange medium of the heat exchanger 40 is the circulationcoolant of the engine; through passing of this circulation coolantthrough its interior, the heat exchanger 40 functions as a heat exchangedevice (see arrows A and A′ in FIG. 1). The circulation coolant that hasattained high temperature as the result of cooling the cylinder blockduring operation of the engine is circulated through a radiator outsidethe engine, and is cooled at the radiator, whereby the temperature ofthe coolant is maintained at approximately 70 to 80 degrees.

(Heating Intake Passage)

Heating intake passage 20 p constitutes a part of the intake passagewhen performing intake air heating, and branches off from a branchingportion 11 b formed on the upstream side of the downstream end 30 b ofthe EGR passage 30 p (with respect to the flowing direction of theintake air) in the intake passage 11 p. The downstream end of theheating intake passage 20 p is formed so as to communicate with theupstream side of the heat exchanger 40 in the EGR passage 30 p (upstreamside with respect to the flowing direction of the EGR gas) at thecommunicating portion 20 b.

(Switch Valve)

The switch valve 11 v serves to adjust the amount of intake air (airfuel mixture) passing through the part of the intake passage 11 p on thedownstream side of the branching portion 11 b (with respect to theflowing direction of the intake air) and through the heating intakepassage 20 p. The air fuel mixture sent from the upstream side to thebranching portion 11 b passes the branching portion 11 b. After that,the proportion in which it circulates through the two circulationpassages of the intake passage 11 p and the heating intake passage 20 p,on the downstream side of the branching portion 11 b, is determined byadjustment of the switch valve 11 v. More specifically, switching iseffected in one of the following patterns: (a) a route in which, on thedownstream side of the branching portion 11 b, all the air fuel mixturepasses through the intake passage 11 p as it is and flows into thecombustion chamber 10 (intake passage: 100%), (b) a route in which, onthe downstream side of the branching portion 11 b, all the air fuelmixture passes through the heating intake passage 20 p to pass through apart of the EGR passage 30 p before passing through the intake passage11 p again to flow into the combustion chamber 10 (heating intakepassage: 100%), and (c) a route which is somewhere between the above tworoutes (i.e., route in which, on the downstream side of branchingportion 11 b, a part of the air fuel mixture passes through intakepassage 11 p, with a part of the air fuel mixture passing throughheating intake passage 20 p).

More specifically, the switch valve 11 v contains a valve (not shown)for the intake passage 11 p and a valve (not shown) for the heatingintake passage 20 p, each of which is controlled to be opened or closed,whereby the respective amounts of intake air passing through the portionof the intake passage 11 p on the downstream side of the branchingportion 11 b and through the heating intake passage 20 p are adjusted.While in this embodiment the switch valve is constructed as describedabove, this should not be construed restrictively.

(ECU)

The ECU 5 controls the switch valve 11 v as follows: First, when the EGRvalve 30 v is closed, the switch valve 11 v is switched such that theair fuel mixture flowing into the combustion chamber 10 passes, on thedownstream side of the branching portion 11 b (with respect to theintake air flowing direction), through at least one of the intakepassage 11 p and the heating intake passage 20 p. On the other hand,when the EGR valve 30 v is open, the switch valve 11 v is switched suchthat the air fuel mixture flowing into the combustion chamber 10 passessolely through the intake passage 11 p on the downstream side of thebranching portion 11 b (i.e., air fuel mixture does not pass throughheating intake passage 20 p, with all the air fuel mixture passingthrough intake passage 11 p).

(Regarding Exhaust Gas and External EGR)

Next, the exhaust gas and the external EGR will be described. Duringhomogeneous charge compression ignition, an abnormal combustion isliable to occur in the operation range on the high load side. In view ofthis, in the homogeneous charge compression ignition engine 1, byopening the EGR valve 30 v in the operation range on the high load side,the EGR gas is cooled by the heat exchanger 40 provided at some midpointin the EGR passage 30 p, and is supplied to the combustion chamber 10together with the air fuel mixture, whereby the combustion in thecombustion chamber 10 is slowed down.

(Regarding Internal EGR)

Next, the internal EGR will be described. The homogeneous chargecompression ignition engine 1 has a negative overlapping period for thevalve timing during homogeneous charge compression ignition operation.Here, the negative overlapping period is a period in which both theexhaust valve 52 v and the intake valve 51 v are closed near the exhausttop dead center, with the exhaust valve 52 v being closed before theexhaust top dead center is reached. As a result, it is possible to allowa part of the already burned gas (internal EGR gas) to remain in thecombustion chamber 10 for the next cycle of combustion. By providing thenegative overlapping period and by utilizing the internal EGR, theinternal EGR gas that is at high temperature is mixed with the air fuelmixture newly supplied into the combustion chamber 10 to increase thein-cylinder temperature, so the ignition property at the time ofhomogeneous charge compression ignition is improved. Further, bycontrolling the length of the negative overlapping period, it ispossible to control the ignition time to some degree.

(Supercharging and External EGR)

Next, supercharging and the external EGR will be described. During highload operation, the supply amount of the air fuel mixture including gasfuel increases, so the ignition property is improved to an excessivedegree, and knocking attributable to too intense a combustion is liableto occur. In order to suppress the occurrence of knocking, it isnecessary to reduce the internal EGR amount in the combustion chamber 10for the purpose of reducing the ignition property. Thus, control iseffected to reduce the negative overlapping period. However, a reductionin the internal EGR simultaneously causes a lag in ignition timing and areduction in combustion rate, so it is impossible to control theignition timing and the combustion rate as they are in a properlybalanced manner. In view of this, the ignition timing is firstcontrolled by raising the intake air temperature through supercharging,maintaining a proper timing. Further, when the engine operation range ison the high load side, external EGR is performed to suppress abnormalcombustion, slowing down the combustion.

(Operation)

Next, an operation of the homogeneous charge compression ignition engine1, constructed as described above, will be illustrated. First, in theoperation range where spark ignition is effected, the ECU 5 controls theignition plug 53 c, etc., thereby effecting spark ignition.

In the operation range where homogeneous charge compression ignition iseffected, the ECU 5 performs the following control. First, the air fuelmixture produced at the mixer 4 passes the intake passage 11 p whilebeing adjusted in intake amount by the throttle 3, and reaches theposition of the branching portion 11 b where the switch valve 11 v isarranged.

Further, when the EGR valve 30 v is closed, the switch valve 11 v isswitched such that the air fuel mixture flowing into the combustionchamber 10 passes at least one of the intake passage 11 p and theheating intake passage 20 p on the downstream side of the branchingportion 11 b. Here, when the air fuel mixture passes the heating intakepassage 20 p, the air fuel mixture passes the heat exchanger 40, so theheating of the air fuel mixture is effected at the heat exchanger 40.Thus, the air fuel mixture, which is at around the outdoor airtemperature, passes the heating intake passage 20 p, and is supplied tothe combustion chamber 10 in a state in which its temperature has beenpreviously raised by several to several tens of degrees. When, forexample, the outdoor air temperature is low, the temperature in thecombustion chamber is low, and it is difficult to obtain a hightemperature internal EGR, so homogeneous charge compression ignitiondoes not easily occur; thus, when homogeneous charge compressionignition is effected, there is a fear of occurrence of a misfire.However, by thus causing a previously heated intake air (air fuelmixture) to flow into the combustion chamber 10, it is possible tosuppress occurrence of a misfire and to enlarge the operation rangewhere homogeneous charge compression ignition is possible.

The case in which the EGR valve 30 v is closed corresponds to the casein which the engine is in the operation range where there is no need touse external EGR. As shown in FIG. 3, an operation range is determinedby engine load and engine RPM; the homogeneous charge compressionignition range (operation range suitable for homogeneous chargecompression ignition) corresponds to the central portion of the drawing.Of this homogeneous charge compression ignition range (including rangesindicated by symbols a, b, c, and d), the ranges a, b, and c areoperation ranges where no external EGR is used.

When the EGR valve 30 v is open, the switch valve 11 v is switched suchthat the air fuel mixture flowing into the combustion chamber 10 passessolely through the intake passage 11 p on the downstream side of thebranching portion 11 b. That is, when the EGR valve 30 v is open, theswitch valve 11 v is controlled such that no air fuel mixture passesthrough the heating intake passage 20 p.

Further, since the EGR valve 30 v is open, a part of the exhaust gasfrom the combustion chamber circulates through the EGR passage 30 p, andis cooled by the heat exchanger 40 before flowing into the intakepassage 11 p from the downstream end 30 b communicating with the intakepassage 11 p and refluxing to the combustion chamber 10. (That is, boththe air fuel mixture and the external EGR gas are sent to the combustionchamber 10). In this way, when the EGR valve 30 v is in the open state,the heat exchanger 40 functions as a cooling device for the externalEGR.

In the high load operation range, abnormal combustion such as knockingor premature ignition occurs; however, by thus utilizing the externalEGR, it is possible to suppress occurrence of abnormal combustion. Morespecifically, the external EGR gas, which is at high temperature (e.g.,approximately 300° C. before reaching the heat exchanger), is cooled bythe heat exchanger (EGR cooler) 40 provided at some midpoint in the EGRpassage 30 p. Further, the cooled EGR gas refluxes into the combustionchamber 10, whereby the combustion in the combustion chamber 10 isslowed down due to an increase in inert gas, and occurrence of abnormalcombustion in the combustion chamber 10 is suppressed.

The case in which the EGR valve 30 is open corresponds to the case inwhich the engine is in the operation range where it is necessary to usethe external EGR. FIG. 3 shows operation ranges that are determined byengine load and engine RPM; of the homogeneous charge compressionignition ranges (ranges a through d), the range d is the operation rangewhere the external EGR is used. More specifically, in the high loadoperation range, the external EGR is utilized as supercharging of theair fuel mixture is effected. As a result, it is possible to both securethe requisite ignition property and slow down the combustion due to anincrease in intake air temperature caused by supercharging and due to alocal reduction in temperature attributable to the external EGR, withthe result that it is possible, in the range on the high load side, toenlarge the range where homogeneous charge compression ignition ispossible.

(Control Example for the Homogeneous Charge Compression Ignition Engineand the Air Intake and Exhaust System)

Next, a control example for the homogeneous charge compression ignitionengine 1 and the air intake and exhaust system 60 will be described withreference to FIG. 2. FIG. 2 is a chart illustrating the opening/closingcontrol and switching control of the EGR valve 30 v and the switch valve11 v of the homogeneous charge compression ignition engine 1. Thehorizontal axis of FIG. 2 indicates the magnitude of the engine load.The upper chart in FIG. 2 illustrates the opening degree of the EGRvalve. In this chart, the lowermost portion (see portion (i) of FIG. 2)corresponds to the state in which the EGR valve 30 v is closed, and theopening degree of the EGR valve 30 v increases as the line extendsupwards therefrom (see portion (ii) of FIG. 2). The lower chart in FIG.2 illustrates how the switch valve 11 v is switched. In this chart, theuppermost position (see portion (1) of FIG. 2) corresponds to the statein which all the air fuel mixture is passing through the heating intakepassage 20 p on the downstream side of the branching portion 11 b, andthe lowermost position (see portion (3) of FIG. 2) corresponds to thestate in which all the air fuel mixture is passing through the intakepassage 11 p on the downstream side of the branching portion 11 b. Theintermediate position (see portion (2) of FIG. 2) corresponds to theintermediate state, that is, the state in which, on the downstream sideof the branching portion 11 b, a part of the air fuel mixture passesthrough the intake passage 11 p, with a part of the air fuel mixturepassing through the heating intake passage 20 p.

Further, as shown in FIG. 2, in the homogeneous charge compressionignition engine 1, the operation range is divided according to theengine load into an NA (natural aspiration) range, a superchargingrange, a supercharging/external-EGR range, etc., and operation controlis effected according to each load range. The horizontal axis in FIG. 2indicates a part of the entire range, which means there exist a range oflower load and a range of higher load than the range shown in thedrawing.

As shown in FIG. 2, in the NA range and the supercharging range, the EGRvalve 30 v is in the closed state, and the heating intake passage 20 pand the intake passage 11 p are used as the intake path. That is, theexternal EGR is not used, but the heat exchanger 40 is used solely forintake air heating.

In the supercharging/external-EGR range, the EGR valve 30 v is in theopen state, and the heating intake passage 20 p is not used at all. Thatis, solely the external EGR is used, and the heat exchanger 40 is usedsolely as the EGR cooler for cooling the external EGR gas.

The control illustrated in FIG. 2 is only shown by way of example; thecontrol of the EGR valve 30 v and the switch valve 11 b is notrestricted to the one shown in the drawing.

(Effects)

In the following, effects of the present invention as compared withthose of a diesel engine will be described. In a diesel engine, intakeair heating is effected for the purpose, for example, of suppressinggeneration of unburned fuel component and white smoke during low loadoperation as in the case of engine start. Further, by using externalEGR, exhaust gas, which is an inert gas, is supplied to the combustionchamber, and the maximum combustion temperature is lowered to reduce theamount of nitrogen oxides generated. To elaborate on this, in the dieselengine, fuel is directly injected into the combustion chamber, sogeneration of differing concentrations of fuel in the combustion chamberis inevitable, whereby a high temperature portion is locally generated,resulting in generation of a large amount of nitrogen oxides. That is,in the diesel engine, external EGR is used for the purpose ofsuppressing generation of nitrogen oxides; in particular, in recentyears, when countermeasures against exhaust gas are being emphasized,the operation range in which it is used along with intake air heating isbeing enlarged in the low load operation range.

On the other hand, in homogeneous charge compression ignition, duringlow load operation as in the case of low outdoor air temperature andduring medium load operation, an improvement in ignition property isachieved by heating the intake air (air fuel mixture), and occurrence ofa misfire is suppressed. Further, in homogeneous charge compressionignition, the use of external EGR during high load operation iseffective in view of suppression of knocking. However, during low loadoperation as in the case of low outdoor air temperature and duringmedium load operation, the use of external EGR is not desirable in viewof deterioration in ignition property. That is, in homogeneous chargecompression ignition, intake air heating helps to achieve an improvementin ignition property and external EGR suppresses ignition property, sothey are used in different operation ranges, which means external EGRand intake air heating are not used simultaneously.

To elaborate on this, in homogeneous charge compression ignition, an airfuel mixture obtained by substantially uniformly mixing fuel and airwith each other is caused to undergo self ignition in the combustionchamber, so, as compared with a diesel engine in which fuel exists in anuneven fashion, and as compared with spark ignition (as in the case of agasoline engine, for example) in which a local high temperature portionis generated in the flame, a local high temperature portion is notgenerated easily, and the maximum combustion temperature is low. Thus,the amount of nitrogen oxides generated is small, and there is no needto use external EGR for the purpose of suppressing generation ofnitrogen oxides.

As described above, in the homogeneous charge compression ignitionengine 1, the use of external EGR and intake air heating are noteffected simultaneously, so the heat exchanger 40 only effects one ofthe cooling of EGR gas and intake air heating according to the operationrange (which is determined according to the engine load and the engineRPM). Thus, due to the above-mentioned construction of the homogeneouscharge compression ignition engine 1, the heat exchanger 40, which isused as the EGR cooler, can also be used for intake air heating withoutinvolving a change in construction, so, even when compared with agenerally adopted construction which uses a single heat exchanger havingonly one heat exchange portion, there is involved no increase in thesize of the heat exchanger. Thus, with the simple construction, it ispossible to effect cooling of the EGR gas and intake air heating.Further, by using an existing EGR passage having an EGR cooler, it ispossible to realize the above-mentioned construction through a change inand addition of a simple piping structure. Further, there is no need toconnect to a single heat exchanger a large number of pipes, includingthe pipes constituting the intake passage and the EGR passage and thepipe for coolant, and the restrictions in terms of design in arrangingthe pipes around the internal combustion engine are mitigated, so it ispossible to achieve further space saving and conduct cooling of the EGRgas and intake gas heating.

Further, in the EGR passage 30 p, the EGR valve 30 v is provided on theupstream side of the downstream end of the heating intake passage 20 p(communicating portion 20 b), so, in the EGR passage 30 p, the heatedintake air (air fuel mixture) is not allowed to flow into the upstreamside of the communicating portion 20 b, and it is possible to reflux theheated intake air to the combustion chamber 10 via the portion of theEGR passage 30 p on the downstream side of the communicating portion 20b and the intake passage 11 p. Further, when the EGR valve is closed, itis possible to prevent EGR gas from flowing into the heating intakepassage 20 p.

Further, the switch valve 11 v is provided at the branching portion 11b, so it is possible to send the intake air (air fuel mixture) heated bythe heat exchanger 40 positively into the heating intake passage 20 p.On the other hand, the intake air (air fuel mixture) not passing throughthe heat exchanger 40 does not enter the heating intake passage 20 p,all of it passing through the intake passage 11 p. Thus, the circulationof the intake air is effected efficiently.

Further, the heat exchanger 40, through which the circulation coolant ofthe engine passes, can utilize the engine heat, making it possible toeffect the cooling of the EGR gas and the intake air heating with astill simpler construction.

Further, with its simple construction, the air intake and exhaust system60 of the homogeneous charge compression ignition device of the presentinvention described above can effect the cooling of EGR gas and intakegas heating. Further, by utilizing an existing EGR passage having an EGRcooler, it is possible to realize the above construction through achange in and addition of a simple piping structure.

(Regarding Expansion of the Range Allowing Operation)

Further, it is possible to expand the range allowing operation towardthe low load side by using the homogeneous charge compression ignitionengine 1 and the air intake and exhaust system 60. This will bedescribed with reference to FIG. 3. FIG. 3 is a schematic viewillustrating the operation range in the case in which the homogeneouscharge compression ignition engine 1 is used; the horizontal axisindicates engine RPM, and the vertical axis indicates engine load.

In FIG. 3, the central portion indicated by symbol HCCI corresponds tothe range where homogeneous charge compression ignition is effected, andthe remaining, peripheral range thereof corresponds to the sparkignition (SI) range. In this way, operation is conducted while effectingswitching as appropriate between homogeneous charge compression ignitionand spark ignition according to the engine load and the engine RPM.

Further, in the case of an engine performing no intake air heating, itis only in the range b in FIG. 3 that operation is conducted by naturalaspiration. That is, when no intake air heating is conducted, operationis conducted through spark ignition in the range a of the drawing.However, in the case in which intake air heating is effected as in thehomogeneous charge compression ignition engine 1, homogeneous chargecompression ignition operation is possible not only in the range b butalso in the range a.

In the following, this will be described more specifically. First, inthe homogeneous charge compression ignition in the range a, which is alow load range, a misfire is liable to occur since the amount of fuelsupplied is small. However, by performing intake air heating in therange a, that is, by closing the EGR valve 30 v and effecting switchingat the switch valve 11 v such that the intake air (air fuel mixture)passes through the heating intake passage 20 p, an improvement inignition property is achieved, and occurrence of a misfire can besuppressed, so homogeneous charge compression ignition is possible. As aresult, it is possible to expand the range allowing operation toward thelow load side.

By performing the above-mentioned control in the homogeneous chargecompression ignition engine 1, it is possible to expand the rangeallowing operation toward the low load side (range a). Further, byadjusting the switch valve 11 v as appropriate, the amounts of intakeair distributed to the intake passage 11 p and the heating intakepassage 20 p are controlled according to the outdoor air temperature,whereby it is possible to adjust the temperature of the intake airflowing into the combustion chamber 10. Thus, irrespective of theoutdoor air temperature, it is possible to expand the operation rangetoward the low load side by adjustment of intake air distribution. Inthe range c of the drawing, operation is effected by supercharging, and,in the range d of the drawing, operation is possible by superchargingand utilization of external EGR.

(Modifications)

Next, modifications of the homogeneous charge compression ignitionengine of the above embodiment will be described with reference to FIGS.4 and 5; the description will center on the differences between theabove embodiment and the modifications. FIG. 4 is an overall schematicview of a homogeneous charge compression ignition engine according to afirst modification, and FIG. 5 is an overall schematic view of ahomogeneous charge compression ignition engine according to a secondmodification. The portions that are the same as those of the aboveembodiment are indicated by the same reference numerals, and adescription thereof will be omitted.

(First Modification)

First, a first modification will be described. As shown in FIG. 4, in ahomogeneous charge compression ignition engine 100 and an air intake andexhaust system 160 according to this modification, a switch valve 111 vand an EGR valve 130 v are provided at the communicating portion 20 bbetween the heating intake passage 20 p and an EGR passage 130 p. Morespecifically, the switch valve 111 v, which is an opening/closing valve,is provided at the connecting portion between the heating intake passage20 p and the EGR passage 130 p, and the EGR valve 130 v, which is anopening/closing valve, is provided in the portion of the EGR passage onthe upstream side of the connecting portion 20 b. Here, a control cable105 d (105 e) connecting the switch valve 111 v and the EGR valve 130 vto an ECU 105 is one obtained by integrating the control cables 5 d and5 e of the above embodiment. In this modification, the switch valve andthe EGR valve are arranged at one position in the form of a valve 100 v,so it is possible to form the homogeneous charge compression ignitionengine and the air intake and exhaust system in a simple construction.

(Second Modification)

First, a second modification will be described. As shown in FIG. 5, in ahomogeneous charge compression ignition engine 200 and an air intake andexhaust system 260 of this modification, an EGR valve 230 v is providednear the communicating portion 20 b (downstream end of the heatingintake passage) between the heating intake passage 20 p and an EGRpassage 230 p, and is provided on the upstream side with respect to theflowing direction of the EGR gas in the EGR passage 230 p. With thisconstruction also, it is possible to obtain the same effect as that ofthe above-mentioned embodiment.

The present invention is not restricted to the above-mentionedembodiment but can be carried out in various modifications withoutdeparting from the scope as defined in the claims.

For example, while in the above embodiment the fuel supply path 2 p isarranged so as to communicate with the portion of the intake passage 11p on the upstream side of the branching portion 11 b, this should not beconstrued restrictively. For example, it may also communicate with theportion of the intake passage 11 p on the downstream side of theconnecting portion (downstream end 30 b) to the EGR passage 30 p (seethe position indicated by arrow C of FIG. 1). By arranging the fuelsupply path 2 p as in the above embodiment or at the position indicatedby the arrow C, it is possible to supply fuel halfway through the routefor intake air no matter which of the intake passage 11 p and theheating intake passage 20 p may be selected by the switch valve 11 v. Onthe other hand, when the fuel supply path is arranged at a position inthe portion of the intake passage 11 p between the branching portion 11b and the connecting portion (downstream end 30 b) (see the positionindicated by arrow B of FIG. 1), the communicating position of the fuelsupply path is not halfway through the route for the intake air when theheating intake passage 20 p is selected, so the fuel supply becomesrather incomplete, which is not desirable.

Further, while in the above embodiment the throttle 3 is arranged in theportion of the intake passage 11 p on the upstream side of the branchingportion 11 b, this should not be construed restrictively; it may also beprovided on the downstream side of the connecting portion to the EGRpassage 30 p (downstream end 30 b) (see the position indicated by arrowC of the drawing). By arranging the throttle 3 at the position of theabove embodiment or at the position indicated by the arrow C, it ispossible to send intake air forwards or suck intake air in from the rearside no matter which of the intake passage 11 p and the heating intakepassage 20 p may be selected by the switch valve 11 v. On the otherhand, when the throttle is arranged at a position in the portion of theintake passage 11 p between the branching portion 11 b and theconnecting portion (downstream end 30 b) (see the position indicated byarrow B of FIG. 1), the adjustment of the amount of intake air becomesrather difficult when the heating intake passage 20 p is selected, whichmeans this arrangement is undesirable.

Further, while in the above embodiment the internal EGR is utilized soas to expand the operation range allowing homogeneous charge compressionignition mainly toward the low load side, and the supercharger 11 t isutilized so as to expand the operation range toward the high load side,this arrangement is not indispensable. When no internal EGR orsupercharger is used, the operation range allowing homogeneous chargecompression ignition is reduced; it is possible, however, to apply thepresent invention in such cases and to utilize intake air heating andexternal EGR. Further, as the device for expanding the operation rangeallowing homogeneous charge compression ignition, there has beenproposed increasing of the compression ratio in the combustion chamberinstead of using internal EGR; the present invention is also applicableto such a homogeneous charge compression ignition engine.

Further, while the above embodiment has been described on the assumptionthat the present invention is to be applied to an internal combustionengine using gas fuel, there are no particular limitations in thisregard; it is also applicable to other types of internal combustionengine such as a gasoline engine. For example, in the case of a gasolineengine, it is possible to use, instead of the mixer of the aboveembodiment, some other fuel supply device such as a carburetor orinjector as appropriate as the fuel supply device.

Further, while in the above embodiment the circulation coolant of theengine is used as the heat exchange medium of the heat exchanger 40,this should not be construed restrictively. For example, when the gasengine of the above-mentioned embodiment is applied to the use of gasheat pump, it is also possible to use the hot water tubing for heatingalready existing in the apparatus. There are no particular limitationsregarding the heat exchange medium to be used as long as it is at atemperature higher than the low outdoor air temperature and lower thanthe temperature of the EGR gas (exhaust gas).

Further, while in the above embodiment the supercharger 11 t is used soas to expand the operation range allowing homogeneous charge compressionignition, this is not indispensable. When it is not so necessary toexpand the operation range allowing homogeneous charge compressionignition toward the high load side, it is also possible to omit thecontrol by the supercharger and the external EGR. The case in which itis not so necessary to expand the operation range toward the high loadside corresponds, for example, to a case in which the operation rangenormally used is restricted to the low and medium load ranges as in thecase of some stationary engines. Further, while it is not so effectiveas in the case in which a supercharger is used, it is also possible toexpand the operation range allowing homogeneous charge compressionignition without using any supercharger as in the case of the range e ofFIG. 6 if the external EGR is also used on the high load side under thecontrol by the internal EGR, that is, in a state in which the internalEGR is reduced, with the amount of air fuel mixture sucked in increased.In FIG. 6, the ranges a, b, and e are ranges in which the amount of theinternal EGR gas is controlled; the range a is a range in which intakeair heating is effected at the time of low outdoor air temperature andlow load to suppress occurrence of a misfire, and the range e is a rangein which the external EGR is also used at the time of high load tosuppress knocking and expand the operation range.

1. A homogeneous charge compression ignition engine, comprising: a combustion chamber; an intake passage serving as a passage for intake air to the combustion chamber; an exhaust passage serving as a passage for exhaust gas from the combustion chamber; an EGR passage, communicating with the exhaust passage and the intake passage, for refluxing a part of the exhaust gas from the combustion chamber to the combustion chamber as an EGR gas; a heat exchanger, provided at some midpoint in the EGR passage, for cooling the EGR gas; an EGR valve, provided at some midpoint in the EGR passage, for adjusting an opening and closing of the EGR passage; a heating intake passage which branches off from a branching portion formed in a portion of the intake passage on an upstream side of a downstream end of the EGR passage and whose downstream end communicates with a portion of the EGR passage on an upstream side of the heat exchanger; a switch valve for adjusting respective amounts of intake air passing through the portion of the intake passage on a downstream side of the branching portion and through the heating intake passage; and a control means which, when the EGR valve is closed, switches the switch valve such that, on the downstream side of the branching portion, the intake air flowing into the combustion chamber passes through at least one of the intake passage and the heating intake passage, and which, when the EGR valve is open, switches the switch valve such that, on the downstream side of the branching portion, the intake air flowing into the combustion chamber passes solely through the intake passage.
 2. A homogeneous charge compression ignition engine according to claim 1, wherein, in the EGR passage, the EGR valve is provided on the upstream side of the downstream end of the heating intake passage.
 3. A homogeneous charge compression ignition engine according to claim 1, wherein the switch valve is provided at the branching portion.
 4. A homogeneous charge compression ignition engine according to claim 1, wherein the switch valve and the EGR valve are provided at a communication portion between the heating intake passage and the EGR passage.
 5. A homogeneous charge compression ignition engine according to claim 1, wherein the heat exchanger is one through which circulation coolant of an engine passes.
 6. An air intake and exhaust system for use in a homogeneous charge compression ignition engine having a combustion chamber and an exhaust passage serving as a passage for exhaust gas from the combustion chamber, the air intake and exhaust system comprising: an intake passage leading to the combustion chamber; an EGR passage, communicating with the exhaust passage and the intake passage, for refluxing the exhaust gas from the combustion chamber to the combustion chamber as an EGR gas; a heat exchanger, provided at some midpoint in the EGR passage, for cooling the EGR gas; an EGR valve, provided at some midpoint in the EGR passage, for opening and closing the EGR passage; a heating intake passage which branches off from a branching portion formed in a portion of the intake passage on an upstream side of a downstream end of the EGR passage and whose downstream end communicates with a portion of the EGR passage on an upstream side of the heat exchanger; a switch valve for adjusting respective amounts of intake air passing through the intake passage and through the heating intake passage on a downstream side of the branching portion; and a control means which, when the EGR valve is closed, switches the switch valve such that, on the downstream side of the branching portion, the intake air flowing into the combustion chamber passes through at least one of the intake passage and the heating intake passage, and which, when the EGR valve is open, switches the switch valve such that, on the downstream side of the branching portion, the intake air flowing into the combustion chamber passes solely through the intake passage. 